Flat resonant element for tr tubes



Sept. 16, 1969 H. GOLDIE 3,467,884

FLAT RESONANT ELEMENT FOR TR TUBES Filed Feb. 13, 1967 C'IRCULATOR 2 1| |o l4 SOURCEOF TRANSMIT- MICROWAVE RECEIVE RECEIVER F|G.l.

ENERGY TUBE ANTENNA l8 i 35 3| m 2 RE m l H 1 IS F IG.2. II ll H z: 1 :1 22

AEZG 24 w 2| ,19 |a l6 w FIG.3.

& FIG.4 Z //////////////////////////A WITNESSES: INVENTOR fiwxmxgg Hurry Goldie United States Patent O US. Cl. 315-39 6 Claims ABSTRACT OF THE DISCLOSURE An extremely low loss resonant element for TR tubes in the form of a flat baflle plate using a single fiat post is described. The element in the form of a fiat baflle plate which extends across a section of rectangular microwave guide and containing a flat tuning cone. An opening adjacent one of the walls of the wave guide constitutes an iris to which an electromagnetic wave energy can be coupled from one side of the iris to the other when the electric field on the wave energy is not suificient to breakdown the discharge gap. A thin flat post, or tongue, having a tapered upper end, extends across the iris opening and means are provided for varying the width of the dis charge gap between the flat end of the tongue and one broadwall of the wave guide.

The present invention relates to transmit-receive devices, commonly called TR tubes, which are connected to the wave guide transmission line between the receiver and the circulator of a radar system to permit the antenna to be time-shared between the transmitter and the receiver without permitting pulses from saturating or degrading the receiver performance but at the same time permitting the weaker echo signal received by the antenna to be coupled into the receiver. Classically, such resonant elements for TR tubes include two opposing cones which are flanked by a pair of iris plates and are located in a gas tight wave guide containing an ionizable gas. The ring-like edges of the conical electrodes form a spark gap which can be broken down by the microwave pulse from the transmitter. To increase its efliciency the gaps enclose an igniter discharge. In accordance with conventional practice this discharge supplements the action of the gaps in causing ionization. It is also conventional to have a negative voltage applied to an electrode near one of the gap electrodes. It is known as the keep-alive electrode and the negative voltage maintains a steady glow discharge that provides a continuous supply of free electrons. When the RF energy from the transmitter is applied to the electrodes the gap fires more quickly. In this manner the keep-alive electrode acts as a cathode while the back of one of the other electrodes acts as the anode.

The resonant element of the prior art TR tubes have been flanked by thin iris plates, as noted previously. The circular configuration of the cones between these plates arises because the tuning is ordinarily accomplished by screw thread adjustment of one of the cones. Heretofore, tuning was also sometimes accomplished by diaphragms. Elimination of circular parts, in accordance with the present invention, is desirable since it reduces the number of and simplifies the required parts. It also facilitates and simplifies the assembly operation. Furthermore, since the circular electrodes have a substantial effective thickness in the direction of the wave propagation they introduce substantial loss relative to an infinitely thin resonant element. It is well understood in the art that in order to minimize loss the resonant plate should be as thin as possible. The flat resonant plate of the present invention makes it possible to substantially reduce the dimension of the element in the direction of wave propagation. The flat plate concept is possible by reason of the novel tuning arrangement of the present invention.

The present invention provides a flat baflle resonant element in TR tubes in which the baffle has an iris with a center post or tongue having a tapered portion terminating in a planar end perpendicular to its axis incombination with means for effectively changing the distance between the planar end of the tapered post and the broadwall of the microwave guide.

It is the object of the present invention to provide a novel and improved resonant element for TR tubes which is simple, easy to assemble, and easy to tune and which provides a minimum of RF loss.

Other and further objects will become apparent from the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic circuit diagram of an environmental radar system in which the present invention may be utilized;

FIG. 2 is a sectional side elevational view of the present invention applied to a wave guide;

FIG. 3 is a sectional plan view on line III-III of FIG. 2, looking in the direction of the arrows; and

FIG. 4 is a profile sectional view of a rectangular wave guide in which another embodiment of the present invention is utilized.

Referring to FIG. 1, a resonant TR tube 10 of the present invention is incorporated into a conventional radar system including a source of microwave energy 11, a circulator 12, an antenna 13, and a receiver 14. The microwave pulses from the source 11 are propagated through arm 12-1 to the antenna 13 by way of the circulator 12 and the TR tube 10 in the wave guide transmission line between the circulator and the receiver 14. Due to a slight mismatch between the circulator and the antenna some microwave energy will be reflected back through the circulator and arm 12-3 to the TR tube 10 which will fire the latter, thus protecting the receiver 14 from the main transmission pulse.

In the embodiment of the invention illustrated in FIG. 2, the resonant element is in the form of a flat baffle plate 16 which is fitted to the inside of the hollow rectangular wave guide 17 in ohmic contact relation therewith. Although the dimensions of the elements are not to scale, it will be noted that in FIG. 3 the thickness of the baffle plate 16 is somewhat greater than the thickness of the side walls of the wave guide 17 but, in general, its dimension in the direction of the propagation of the microwave energy is very small compared to the normal operating wavelength of the wave guide. It is this essential characteristic which lowers the loss over conventional TR resonant elements.

The plate 16 is provided with a rectangular notch 18, which in this instance, is adjacent the upper broadwall of the wave guide. In order to tune the iris, formed by the rectangular notch 18, to the operating frequency a movable flat post or tongue 19 is slidably engaged in a rectangular opening 21 which extends from the bottom of the notch 18 to the bottom of the baffle plate 16. In alignment with the opening 21 in the bame plate, there is an opening 22 in the lower transverse wall of the wave guide 17. The rectangular opening 21 in the baflle plate 16 and the opening 22 in the wave guide side walls should provide a close tolerance fit with the lower body of the post 19 in order to avoid lateral motion. The lower end of the post 19 is provided with a projection 24 which is supported on a flexible wire 26 which is in turn secured to depending posts 27 and 28 affixed to the bottom wall of the wave guide. The upper end of the post 19 is tapered and has a planar end 31 perpendicular to the longitudinal axis of the post which primarily forms a capacity coupling with the broadwall of the wave guide in order to tune the wave guide to the desired resonant frequency and form a resonant discharge gap 35. Means in the form of a diaphragm may be provided for supporting or moving the post 19 toward and away from the upper transverse wall of the wave guide in order to adjust the resonant discharge gap between the wall of the wave guide and the flat planar surface 31 at the end of the post. The post may be held in desired adjusted position for tuning the discharge gap 35 by epoxy resin, or the like.

An alternative form of the invention is illustrated in FIG. 4 wherein a bafile plate 41 has its edges ohmically connected to the inner surface of the rectangular wave guide 42. The battle plate 41 has a thin tapered flat post 43 integral with and extending upwardly from the bottom of a rectangular notch 44 to a point near the upper broadwall of the wave guide to form a resonant frequency gap 46, also known as a resonant discharge gap. In this embodiment, the post 43 is not adjustable but the adjustable resonant frequency gap is provided by distorting the upper transverse side wall of the wave guide 42 toward the upper planar end of the post 43. This may be accomplished by means of an adjusting screw 47 which threadedly engages a U-shaped bracket 48 supported in a recess 49 in the upper broadwall of the wave guide 42. As an alternative, in the recess 49 a separate flexible metal disc such as a diaphragm, may be inserted under the lower end of the screw 47 which forms a portion of the broadwall of the wave guide immediately adjacent the resonant frequency gap.

It will be seen that the geometric simplicity of the resonant elements of the present invention leads to desirable low loss microwave properties, as well as simplification of the assembly techniques. The utility of this novel design is illustrated by experimental data. As an example, a device according to this invention was fabricated for operation in the X-band and was fabricated by using a resonant element similar to that shown in FIG. 4 in which the bafile opening 44 was 0.080 inch by 0.450 inch. By tuning the radio frequency gap from two to six milli-inches the resonant frequency varied from 9.25 to 9.75 gHz. at a relatively constant Q of 6.3. With a 0.006 inch gap the resonant element was heated from 25 C. to a temperature of 100 C. with a resultant 0.5% decrease in the resonant frequency which indicates good temperature stability. The insertion loss was 0.01 db, a relatively low figure, and the simulated isolation was approximately 28 db.

It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the present invention. For example, some departure could be made from the preferred embodiment wherein opening 21 in the baffle plate 16 need be only deep enough to guide and accommodate the adjustment movement of the center post 19. Then a rod or any suitable extension, corresponding to projection 24 could be extended through a smaller opening to and through the bottom broadwall of the wave guide.

Also it will be understood that the usual keep-alive electrode would be used with the present invention in a manner well understood in the art. Since such a keep-alive electrode would not cooperate with the present invention in any special way different from the prior art, the keepalive assembly is not illustrated or described.

I claim as my invention:

1. A low loss resonant frequency discharge gap comprising a section of four sided hollow wave guide, an iris plate extending transversely across said wave guide and having a notch in one broad edge thereof, the remaining edges of said plate being in ohmic contact with the inner surfaces of the wave guide walls, a tuning post having a rectangular cross section supported on said plate and having a portion extending from the bottom of said notch toward the adjacent wall of said wave guide and being tapered with the terminus of said post being planar and forming a resonant discharge gap in conjunction with the wall of said wave guide facing said notch, the dimension of said post in the direction of the axis of said wave guide being very small as compared to its dimension transverse to said wave guide.

2. The combination as set forth in claim 1, in which said post is adjustable relative to said iris plate.

3. The combination as set forth in claim 1, in which said iris plate has a rectangular opening to slidably receive said post so that it may be adjustably supported by said iris plate with its planar end positioned relative to the broadwall of said wave guide facing said notch to tune the resonant discharge gap.

4. The combination as set forth in claim 3, in which said rectangular opening in said iris plate extends from the bottom of said notch to the opposite broad edge of said plate, with said tuning post slidably engaging said opening and having a projection extending through an opening in the second broadwall of said wave guide and means carried by said wave guide for supporting said projection.

5. The combination as set forth in claim 1, with means for adjusting the distance between the terminus of said post and the adjacent broadwall of said wave guide.

6. The combination as set forth in claim 5 in which said adjusting means includes means for distorting the adjacent broadwall of said wave guide toward the terminus of said post.

References Cited UNITED STATES PATENTS 2,415,962 2/1947 Okress 333-43 2,524,268 10/1950 McCarthy 3 l5-39 2,939,043 5/1960 Fallon 31539 HERMAN K. SAALBACH, Primary Examiner S. CHATMON, JR., Assistant Examiner U.S. Cl. X.R. 313148; 33313 

